We report the filling fraction limit in filled Skutterudites plays a critical role in thermoelectric properties; however, the exact filling fraction limit for certain fillers is still in debate. In this work, we observed the lattice distortion, where lattice parameters a and b are unequal, in the annealed Yb-filled CoSb 3. Microstructure characterization by advanced spherical aberration-corrected (C S-corrected) electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy in conjunction with thermoelectric characterization clearly proves that the Yb filling fraction is higher in the annealed sample (with lattice distortion) than in the ball-milled sample (without lattice distortion). Therefore, the results indicate that lattice distortion appears when the Yb filling fraction reaches a certain critical value in CoSb 3 Skutterudites. Lastly, the observed lattice distortion provides an alternative approach to probe the filling fraction in filled Skutterudites.

The complex doping behavior of Ga and In in CoSb 3 has been investigated using ab initio total-energy calculations and thermodynamics. The formation energies of void filling, Sb substitution and complex dual-site occupancy defects with different charge states, and their dependence on chemical potentials of species, were studied. Results show that Ga predominantly forms dual-site 2Ga VF–Ga Sb defects and substitutes for Sb only at very high Fermi levels or electron concentrations. In, on the other hand, can play multiple roles in skutterudites, including filling in the crystalline voids, substituting for Sb atoms or forming dual-site occupancy, among which themore » fully charge-compensated dual-site defects (2In VF–In Sb and 4In VF–2In Sb) are dominant. The equilibrium concentration ratio of impurities at void-filling sites to those at Sb-substitution sites for Ga-doped CoSb 3 is very close to be 2:1, while this value markedly deviates from 2:1 for In-doped CoSb 3. Furthermore, the 2:1 ratio of Ga doping in CoSb 3 leads to low electron concentration (~2 × 10 19 cm –3) and makes the doped system a semiconductor.« less

Filling voids with rare earth atoms is an effective way to lowering thermal conductivity which necessarily enhances thermoelectric properties of skutterudite compounds. Yb atom is one of the most effective species among the rare earth atoms for filling the voids in the skutterudite structure due to a large atomic mass, radius and it is intermediate valence state. In this work, we aim to find the best filling partners for Yb using different combinations of Ce and In as well as to optimize actual filling fraction in order to achieve high values of ZT. The traditional method of synthesis relying onmore » melting-annealing and followed by spark plasma sintering was used to prepare all samples. The thermoelectric properties of four samples of Yb{sub 0.2}In{sub 0.2}Co{sub 4}Sb{sub 12}, Yb{sub 0.2}Ce{sub 0.15}Co{sub 4}Sb{sub 12}, Yb{sub 0.2}Ce{sub 0.15}In{sub 0.2}Co{sub 4}Sb{sub 12}, and Yb{sub 0.3}Ce{sub 0.15}In{sub 0.2}Co{sub 4}Sb{sub 12} (nominal) were examined based on the Seebeck coefficient, electrical conductivity, thermal conductivity, and Hall coefficient. Hall coefficient and Seebeck coefficient signs confirm that all samples are n-type skutterudite compounds. Carrier density increases with the increasing Yb+Ce content. A high power factor value of 57.7 {mu}W/K{sup 2}/cm for Yb{sub 0.2}Ce{sub 0.15}Co{sub 4}Sb{sub 12} and a lower thermal conductivity value of 2.82 W/m/K for Yb{sub 0.2}Ce{sub 0.15}In{sub 0.2}Co{sub 4}Sb{sub 12} indicate that small quantities of Ce with In may be a good partner to Yb to reduce the thermal conductivity further and thus enhance the thermoelectric performance of skutterudites. The highest ZT value of 1.43 was achieved for Yb{sub 0.2}Ce{sub 0.15}In{sub 0.2}Co{sub 4}Sb{sub 12} triple-filled skutterudite at 800 K. - Graphical abstract: Thermoelectric figure of merit of Yb{sub x}In{sub y}Ce{sub z}Co{sub 4}Sb{sub 12} (0{<=}x,y,z{<=}0.18 actual) compounds versus temperature. Highlights: Black-Right-Pointing-Pointer TE properties of Yb,In,Ce multiple-filled Yb{sub x}In{sub y}Ce{sub z}Co{sub 4}Sb{sub 12} skutterudites were investigated. Black-Right-Pointing-Pointer Thermal conductivity is strongly suppressed by multiple filling of Yb, Ce and In. Black-Right-Pointing-Pointer Small amounts of Ce and In with Yb are beneficial for the enhancement of TE performance. Black-Right-Pointing-Pointer The highest ZT=1.43 was achieved with Yb{sub 0.07}In{sub 0.094}Ce{sub 0.065}Co{sub 4}Sb{sub 11.92} at 800 K.« less

La 3Co 4Sn 13 and La 3Ru 4Sn 13 were categorized as BCS superconductors. In a plot of the critical field H c2 vs T, La 3Ru 4Sn 13 displays a second superconducting phase at the higher critical temperature T c*, characteristic of inhomogeneous superconductors, while La 3Co 4Sn 13 shows bulk superconductivity below T c. We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds. Additionally, for La 3Ru 4Sn 13 we find that T c*/dP>dT c/dP. The pressure dependences of T c are interpreted according to the McMillan theory and understood tomore » be a consequence of lattice stiffening. The investigation of the superconducting state of La 3Co xRu 4–xSn 13 shows a T c* that is larger then T c for x < 4. Furthermore, this unique and unexpected observation is discussed as a result of the local disorder and/or the effect of chemical pressure when Ru atoms are partially replaced by smaller Co atoms.« less